The invention relates to the field of glycerols. In particular, the invention relates to a method for the preparation of a composition comprising diglycerol, and optionally, polyglycerols. The composition does not comprise undesirable cyclic glycerol compounds.
German Patent DE-OS 3,900,059 discloses a process for the preparation of polyglycerol, in which process .alpha.-monochlorohydrin is reacted with epichlorohydrin at temperatures of from 20.degree. to 120.degree. C. The molar ratio of epichlorohydrin to .alpha.-monochlorohydrin is from 0.8:1 to 1:2.5. They are reacted in the presence of acids or compounds which have an acidic reaction. The reaction mixture then is reacted with a medium in an alkaline reaction. Water is then added, and the product is demineralized by one or more cation exchangers and subsequent anion exchangers, and is separated by distillation into diglycerol and, if appropriate polyglycerol.
The shortcoming of this process is that the amounts of triglycerol, tetraglycerol and higher polyglycerols as well as the amount of cyclic components are relatively high when .alpha.-monochlorohydrin is reacted with epichlorohydrin. Moreover, a chlorine-containing compound which contaminates the polyglycerol is formed as a secondary product which can only be hydrolyzed with difficulty.